Display devices, such as liquid crystal display (LCD) devices, are used in a variety of applications including, for example, televisions, hand-held devices, digital still cameras, video cameras, and computer monitors. Unlike a traditional cathode ray tube (CRT), an LCD panel is not self-illuminating and, therefore, sometimes requires an illumination assembly or a “backlight.” A backlight typically couples light from one or more light sources (e.g., cold cathode fluorescent tubes (CCFTs) or light emitting diodes (LEDs)) to an LCD panel.
Two common types of backlights are direct-lit backlights and edge-lit backlights. These two types of backlights differ in the placement of the light source(s) relative to the output face of the backlight, where the output face defines the viewable area of the display device. In edge-lit backlights, a light source or light sources are disposed along an outer border of the backlight construction, outside the area or zone corresponding to the output face of the backlight. The light source(s) typically emit light into a light guide, from which light is extracted to illuminate the output face of the backlight. In direct-lit backlights, one or more light sources are disposed directly behind the output face of the backlight.
The performance of an LCD is often judged by its brightness. However, the viewing experience of a display may be compromised if the degree of brightness varies across its viewable area. This may occur where discrete light sources are used in the backlight due to the reduction of brightness with increased distance from the light source(s). Various arrangements have been proposed to combat this problem. For example, in direct-lit displays thick diffuser plates have been used to mix the light from individual light sources. In edge-lit displays, extraction dots have been placed closer together to provide increased extraction of light with increased distance from the light source(s). These solutions, however, result in loss of light due to scattering and absorption.